The present invention relates generally to cooling devices and, more particularly, to cooling devices for removing heat from electronic devices by a flow of gas, in particular, airflow, said flow being produced by a blower.
During normal operation, most electronic devices generate significant amounts of heat. If this heat is not continuously removed, the electronic device may overheat, resulting in damage to the device and/or a reduction in operating performance.
In order to avoid such problems caused by overheating, cooling devices are often used in conjunction with electronic devices.
One such cooling device used in conjunction with electronic devices is a fan assisted heat sink. In such device, a heat sink is formed from a material, such as aluminum, which readily conducts heat. The heat sink is usually placed on top of, and in physical contact with, the electronic device.
One method of increasing the cooling capacity of these heat sinks is by including a plurality of cooling fins that are physically connected to the heat sink. These fins serve to increase the surface area of the heat sink and, thus, maximize the transfer of heat from the heat sink to the ambient air. In this manner, the heat sink draws heat away from the electronic device and transfers the heat to the ambient air.
In order to further enhance the cooling capacity of a heat sink device, an electrically powered blower (an axial fan may serve as the blower) is often mounted within or on top of the heat sink. In operation, the fan forces air to pass over the fins of the heat sink, thus, cooling the fins by enhancing the heat transfer from the fins into the ambient air. As the fins are cooled, heat can be drawn from the electronic device and into the heat sink at a faster rate. The fan typically draws air into the heat sink from the top of the heat sink, passes the air over the fins, and exhausts the air from the heat sink in the vicinity of the bottom (side) of the heat sink. Accordingly, the exhaust air is hotter than the intake air.
There are known devices of this typexe2x80x94see, for example, U.S. Pat. No. 5,867,365 xe2x80x9cCPU heat sink assemblyxe2x80x9d and U.S. Pat. No. 5,661,638 xe2x80x9cHigh performance spiral heat sinkxe2x80x9d.
The design of the device described in U.S. Pat. No. 5,867,365 comprises an axial fan that produces a flow passing by heat exchanging channels of the heat sink. The majority of inlets to heat exchanging channels are located just opposite the axial fan""s impeller with a certain number of said channels being placed radially in relation to fan axle.
U.S. Pat. No. 5,661,638 also involves the application of an axial fan. Specific embodiment of device claimed in said patent involves such placement of heat exchanging channels of the heat sink that they are located centrally-symmetrically about the fan axle. To increase the heat exchange area, the heat exchanging channels are made of spiral-like shape and bent backwards in the direction of blower rotation. In this case the fan is installed in a recess made in the heat sink body.
In the above-mentioned designs, the axial fan produces sufficient air pressure. However, due to the weak airflow in the area adjacent to the fan axle, the conditions for cooling the central part of the heat sink, located underneath the fan, are unfavorable. In this case uniform cooling of the heat sink and electronic device, such as a processor, will not take place. The energy of airflow outgoing from fan impeller, in the axial direction, is expended on deceleration and change in flow direction before entering to the heat exchanging channels. This decreased airflow velocity, passing by the heat exchanging channels doesn""t allow good conditions for the heat exchange process.
Centrifugal blowers are rarely used in cooling device designs for the purpose of producing airflow.
Specifically, U.S. Pat. No. 5,838,066 xe2x80x9cMiniaturized cooling fan type heat sink for semiconductor devicexe2x80x9d offers a design employing a centrifugal blower that is installed to the side of the heat sink. In one particular embodiment of this invention the cooling airflow passes by rectilinear heat exchanging channels of the heat sink.
However, placement of the centrifugal blower to the side of the heat sink increases the device size. The location of the centrifugal blower leads to poor coordination between the airflow produced by the blower and the direction of the inlet channels of the heat sink. The loss in airflow energy results in the reduction of airflow speed in the heat exchanging channels and in the decline of heat exchange efficiency. A portion of energy, of the airflow, is also expended in the form of friction against the casing enclosing the blower.
An invention described in the patent of Japan No. 8-195456 entitled xe2x80x9cCooler for electronic apparatusxe2x80x9d. This device comprises a centrifugal fan enclosed in the casing and installed above the heat exchanging channels that are made divergent. Another heat sink surface is made so that the possibility of thermal contact with an electronic device is provided for. The inlet of the centrifugal fan faces the heat sink. The fan produces an airflow that passes by heat exchanging channels and then gets drawn into the inlet of the centrifugal fan. Since the centrifugal fan operates by drawing air in to the heat sink, there is an area in the central part of the heat sink that that receives poor airflow movement. This can be seen in the published patent. Therefore, cooling of the heat sink""s central part, which is the hottest, is ineffectively performed and results in uneven cooling of the heat sink. To avoid uneven cooling of the heat sink, one has to raise the fan power in order to increase the airflow. In addition, the device is of considerable height because of the centrifugal fans placement above the heat sink, and the electric drives placement above the centrifugal fan.
Increasing the size of the cooling device in a vertical direction (i.e. in a direction transverse to the orientation of the integrated circuit device) is often a problem because of the limited envelope available in many applications, such as in the computer case of a desktop computer and especially for portable electronic devices such us laptop computers. This is an even greater problem because, in most situations, a fairly substantial clearance area is required between the fan opening and the computer case to allow adequate airflow into or out of the fan.
Thus, it would be generally desirable to provide an apparatus, which overcomes these problems associated with fan assisted heat sink devices.
Accordingly, it is an object of the present invention to provide a cooler that achieves more uniform cooling of electronic devices by more effective cooling of the central part of the heat exchange element.
It is another object of the present invention to provide a cooler with an overall reduction in height and in doing so allow for a reduction of the cooling device size.
It is further an object of the present invention to provide an electric motor combined with a heatsink that has a significant reduction in overall height.
In order to achieve these objectives the following described cooler design is needed. According to the present invention, a cooler for electronic devices comprises a heat exchange element, a blower with a radial type impeller, and an electric drive, wherein said heat exchange element comprises heat exchanging means made on one surface of said heat exchange element while its other surface provides thermal contact with a heat-radiating means, said radial type impeller has a shroud with a flat surface from one side, a hub and brackets and a central inlet between the shroud and the hub, said brackets connect the hub with the shroud, said radial type impeller is positioned on the heat exchange element so that the heat exchanging means being surrounded by the radial type impeller and a cooling gas flows to the radial type impeller from the central inlet through the heat exchanging means, said electric drive comprises a magnetic rotor and a stator; said magnetic rotor is a flat diskxe2x80x94type rotor comprises a central hole inside the disk and circumferential arrayed like poles, said stator comprises circumferential arrayed coils, axis of said coils are parallel to the axis of rotation, said coils mounted around of the circumferential arrayed like poles. Said magnetic rotor is placed on the shroud of the radial type impeller and connected with the shroud, the shaft of the electric drive is located inside the hub of the radial type impeller, and the central hole of the flat disk type rotor coincides with the central inlet.
Further said magnetic rotor comprises at least two magnetized rings each having circumferential arrayed like poles and being mounted perpendicularly to the axis of rotation, and said circumferential arrayed like poles of one of the magnetized ring being magnetized in opposite polarity and coincide to the circumferential arrayed like poles of another magnetized ring in a projection at a plane normal to the axis of rotation, said at least two flat rings installed with a gap between said flat rings in a place, where the magnetic rotor interacts with the stator and with a contact between said flat ring axially beyond the gap, said coils of said stator at least partially mounted at the gap between the circumferential arrayed like poles of one of the magnetized ring and the like circumferential arrayed poles of the another adjacent magnetized ring. A cylindrical magnet that is magnetized in the axial direction may be placed coaxially to the shaft between said magnetized disks. The heat exchanging means are pins and fins, and the heat-exchange element is made from a high heat-conducting material. The heat-radiating means may be a heat-pipe.
One of the flat rings of the magnetic rotor is placed flush-mounted with the flat surface of one side of the shroud of the radial type impeller.
Flat rings are magnetized in a such way that the poles of each flat rings are like poles, while in relation to the poles of the other flat ring they are unlike poles, the magnetic rotor poles are made up by teeth on the outer circumferences of said flat rings, said teeth coincide along the direction of said rotation axis.
The stator poles are placed in the space between the said magnetic rotor poles of each disk.
In addition, the cooler for electronic devices may comprise the heat exchange element that has heat exchanging fins and/or pins and heat exchanging channels.
Said heat exchanging fins and/or pins are surrounded by the radial type impeller, said radial type impeller is surrounded by said heat exchanging channels and a cooling gas flows from the central inlet through the heat exchanging fins and/or pins, the radial type impeller and the heat exchanging channels in a series way.
The heat exchanging channels may be formed by rows of profiled elements; said profiled elements may be made in the form of pins and/or fins. The heat exchanging channels may be made spiral-like and bent in the direction of blower rotation, and inlets of the heat exchanging channels are oriented in the direction of propagation of an output of the cooling gas flow produced by the radial type impeller. The heat exchanging channels may be made of constant width.
The stator may be made like a printed circuit board, said printed circuit board covers the heat exchanging channels from the opposite side of the surface, which provides thermal contact with the heat-radiating means.
Next, the electric drive for cooler for electronic device comprises a stator, a magnetic rotor and a motor controller. Said magnetic rotor comprises at least two magnetized rings having circumferential arrayed like poles and are mounted perpendicularly to the axis of rotation, and said circumferential arrayed like poles of one of the magnetized ring are magnetized in opposite polarity and coincide to the circumferential arrayed like poles of another magnetized ring in a projection at a plane normal to the axis of rotation. Said at least two flat rings installed with a gap between said flat rings in a place, where the magnetic rotor interact with the stator and with a contact between said flat ring axially beyond the gap. Said stator comprises circumferential arrayed coils, axis of said coils are parallel to the axis of rotation, said coils at least partially mounted at the gap between the circumferential arrayed like poles of one of the magnetized ring and the like circumferential arrayed poles of the another adjacent magnetized ring.
One of the flat rings of said magnetic rotor is placed on an additional flat ring made from nonmagnetic material and said additional flat ring being connected by brackets with a shaft of the electric drive. The brackets may be made in the form of axial blower blades. One of the flat rings of the magnetic rotor is placed flush-mounted with the flat surface of one side of the shroud of the radial type impeller. The flat rings are magnetized in a such way that the poles of each flat rings are like poles, while in relation to the poles of another flat rings they are unlike poles, the magnetic rotor poles are made up by teeth on the outer circumferences of said flat rings. A cylindrical magnet, which is magnetized in the axial direction, is placed between the flat rings. The stator may be made like a printed circuit board.
To prevent additional noise caused by the pulsation of pressure of the cooling flow at the inlets of the heat exchanging channels, it is advisable to install the centrifugal blower impeller with a radial gap of no less than 0.03d (where d is the diameter of centrifugal blower impeller) in relation to the inlets of the heat exchanging channels.
The heat exchanging channels covered with the stator plate from above. In this case the cooling airflow will propagate only along the channels.
A disk-type centrifugal blower with at least one disk is used in the design. The disks are installed in such manner that the edge of disk surface facing the heat exchange element is located opposite the inlets to the heat exchanging channels.
The centrifugal blower supplies cooling flow (for instance, airflow) to the central part of the heat exchange element, which fact facilitates the effective cooling of the hottest part of the heat exchange element. Transfer of energy from blower disk to the airflow proceeds due to the friction forces.
The airflow movement in the central part of the heat exchange element is not only in the radial direction, but also in the tangential direction. This allows for an additional increase in airflow velocity in the central part of the heat sink to take place resulting in a gain in cooling efficiency.
Since the edges of blower disk surfaces facing the heat exchange element are located opposite the inlets to the heat exchanging channel, the cooling flow is supplied to said inlets and as the airflow passes by the channels it cools the heat exchange element down. The disk-type centrifugal blower generates a radial airflow that matches the inlets to the heat exchanging channels.
The disk-type centrifugal blower is characterized by its small size (in terms of height) while being effective enough to perform as a cooling fan. It is also characterized by having low noise levels as compared to other types of centrifugal blowers with all other factors being equal.
The above-mentioned specific features of the device claimed herein provide for a special cooling pattern, which is characterized by the fact that the hottest part of the heat exchange element (namely, its central part) gets cooled first, and, as compared to the above-described prototype, the entire cooling process proceeds more evenly and without losses that are caused in said prototype by flow turn and friction when the cooling flow (going from the blower disk) enters the heat exchanging channels. As a consequence, when using the invention being claimed one would need a blower of lesser power and size.
In addition, the surface of at least one of the disks of the disk-type centrifugal blower (facing the heat exchange element) may be equipped with radial projection that increase the radial component of the airflow.
Axial blower blades may be installed on at least one of the disks of the centrifugal blower near its central opening; said blades being attached to the disk. The blades may be installed on one disk or on several disks. Installation of the axial blower blades near the central opening of the disk increases the pressure of cooling airflow in the central part of the heat exchange element with the blower capacity being the same. Such a design of the disk-type centrifugal blower coupled with installation of the axial blower blades makes it possible to attain the same blower capacity with a lower number of revolutions, which fact results in additional decrease in noise level generated by the blower.
According to one embodiment, the axial blower blades may be used as straps that secure disk on the axle of the centrifugal blower.
For the purpose of increasing the heat exchange area, the heat exchanging channels can be made in the form of rows of profiled elements. In particular, these elements can be made in the form of substantially circular shaped pins fins.
As a particular embodiment of the invention, the heat exchanging channels may be made spiral-like and bent in the direction of centrifugal disk blower rotation. This will provide for the prolonged contact between the airflow and heat exchange element surface. In the latter case the heat exchanging channels may be made of constant width. This will make it possible to ensure the constancy of velocity at which the airflow blows the surfaces of heat exchanging channels, making heat exchanging channels of constant width would enable one to attain the maximum xe2x80x9cdensityxe2x80x9d of heat exchanging channels on the heat exchange element surface, which would result in obtaining greater heat exchange area.
When making heat exchanging channels spiral-like especially when they are made of constant width it is advisable to orient their inlets in the direction of the propagation of the output flow produced by disk centrifugal blower. In this case the best matching between the channels and incoming airflow is attained, that would sustain the airflow velocity at the maximum possible level.
In addition, the heat exchanging channels covered with the stator plate from above secured to the surface of the heat exchange element. In this case the entire cooling airflow will propagate only along the channels that also facilitates the improved heat exchange.